I read somewhere on this website that you should start a omen journal. This got my mind thinking and wondering if there are any good books/websites that go into greater detail about omens, what they mean, what may happen, how to know if its a omen ext .

I would look into your region's folklore and superstitions. Then, I would start trying to apply it in practice, say reading candle wax or clouds. Slowly build on that practice, understand them, maybe find some through personal experience.